Atomic frequency standard using digital processing in its frequency lock loop

Abstract

A passive atomic frequency standard such as a Rubidium Frequency Standard or a Cesium Frequency Standard, using a microprocessor or equivalent circuit as part of its Frequency Locked Loop. The microprocessor phase modulates (pm) the RF signal which is introduced into the Atomic Resonator, and demodulates the output signal. The modulation and demodulation are performed by frequency hopping or spread spectrum techniques. Secondly, the microprocessor samples and integrates the error signal from the atomic resonator (Physics Package or Atomic Tube) with a sampled weighted- sum technique and thus better filters the noise, improves the Signal to Noise Ratio, rejects large noise like spikes, etc. Thirdly, the microprocessor saves the last control voltage of the Voltage Controlled Oscillator (VCO) to ease the start-up of the device as well as to keep the VCO at the last frequency in case the atomic resonator fails to function.

We claim: 
     
       1. An atomic frequency standard comprising a frequency lock loop circuit containing a microprocessor or equivalent intelligent circuit, adapted to modulate the RF input to an atomic resonator and to demodulate an error signal by means of frequency hopping or by a spread spectrum techniques. 
     
     
       2. A standard according to claim 1 where the microprocessor is adapted to sample averages and to integrate the error signal from the atomic resonator, utilizing a weighted average to improve the signal to noise ratio and to reject disturbances. 
     
     
       3. A method of operating a passive atomic frequency standard which standard comprises using a microprocessor as part of its frequency lock loop for modulating the RF signal introduced into the atomic resonator and demodulating an output signal from the atomic resonator by frequency hopping or by a spread spectrum technique. 
     
     
       4. A method according to claim 3, where an error signal is integrated by the microprocessor using a weighed sum technique, thus filtering out noise and improving the signal-to-noise ratio and rejecting disturbances. 
     
     
       5. A method according to claim 3 where the microprocesser produces a control voltage for a VCO and the last control voltage is saved in order to facilitate the start up of the device and in order to keep the VCO at the last frequency in case of atomic resonator failure.